Leishmania secretory factor GP63 targets the DICER1/miR-122/hepcidin axis in host macrophages to deplete Nramp1

Abstract

Micronutrient sequestration is a powerful host defence mechanism against intracellular pathogens. Central to this is the iron transporter Nramp1, which actively effluxes iron from phagolysosomes, depriving the engulfed pathogens of this essential element. Leishmania have evolved a clever strategy to counteract this by triggering hepcidin-mediated proteasomal degradation of Nramp1. Interestingly, treatment with Leishmania major conditioned media induced hepcidin upregulation and Nramp1 degradation even in uninfected macrophages, with simultaneous increase in endo/lysosomal iron content. This suggested the involvement of a parasite-derived secretory factor, ultimately leading to the identification of the metalloprotease GP63 as the effector responsible for Nramp1 degradation. Conditioned medium from the GP63 knockout strain (LmGP63-/-) failed to upregulate hepcidin expression or promote Nramp1 degradation. Further, we show that GP63 depletes DICER1 in macrophages, blocking maturation of miR-122, a known negative regulator of hepcidin. These in vitro findings were validated in a mouse model, where the wild type L. major, but not the LmGP63-/- strain, could deplete DICER1, induce hepcidin expression and reduce Nramp1 levels in the infected tissue. Collectively, we uncover a novel role for Leishmania GP63 in targeting the DICER1/miR-122 axis in host macrophages to trigger hepcidin expression and Nramp1 degradation, thereby facilitating iron acquisition by the parasite.